Mutations and Birth Defects
Any species of sentient life on Xiunus may have what is called a Mutation - an alteration in their form or abilities caused by either natural or unnatural causes.
Breeding
Any breeding has a chance of producing mutated offspring. The chance is low, but there. Breedings involving one or both mutated parents may result in a higher chance of mutated offspring. Also, inbred pairings have higher chances of mutated offspring as well as birth defects, which often can cause harm to a whelp or reduce their stats in some way.
Certain researches and items can increase the chances for or even guarantee mutations in breedings, though often these have limits on usage or are consumed in a breeding.
Unnatural Means
There are... other ways to have a colonist have mutations. These can occur outside of the breeding process and an existing colonist may one day suddenly have a mutation they didn't have before. Usually, this is done by the use of potions and tinctures, such as the Tincture of Mycelium which adds the Mycelium mutation, and the XYZ which can add any common mutation to a colonist in a design request.
Most mutations have no effect on game play. They are generally more aesthetic than anything else.
Designing Mutations and Birth Defects
Oftentimes, mutations and birth defects of the same type may display differently from others. For instance, two colonists may both have "extra limbs" but one may have additional arms while the other has an extra tail. We want to encourage creativity in this and thus have no official lineart of the individual mutations and birth defects, save a few specifically requested for or commissioned for the site. We allow users to create and share edits of the official lines with others freely.
If you are having trouble editing lineart or creating your own with your mutation in mind, feel free to mention in the discord! Our community is very friendly and helpful and more likely than not, someone will offer to help you out - perhaps for free, perhaps for a few pieces of their colonists, etc.
Editing Lineart
The easiest way I (Xione) have found to edit lineart for mutations is to look at the transparent lines on an art program that allows layers and lower their opacity. In a new layer, I sketch the mutations on, then lower the opacity of that layer. In another layer, I line the sketch, being careful to try to keep the visual style of the original line art I'm working from. After the mutation pieces are lined and the sketch layer is deleted, I erase the conflicting areas on the original line art (such as where the back or ears, etc, may overlap with the mutation) and put opacity back to 100%. Then, I merge the two lineart layers into one Line layer.
On another layer beneath the Line layer, which I call the Colour layer, I fill with a base colour. Then in the Line layer, I use the Magic Wand (Area Select, etc) tool to select all large areas outside of the line art. I "expand" this selection by one or two pixels and then delete that area on the Colour layer.
After this, there are various options. If your art program allows for Clipping Layers, I add a clipping layer above the Colour layer and begin working on the design. Another option is to have the colour and marking layers be masked to the shape of the Colour layer. It's really up to you at this point!